This invention relates to gas turbine technology and, more specifically, to a liner system for internally insulated, high velocity gas turbine exhaust diffusers.
Current high velocity diffusers are externally insulated, smooth wall, hot shell structures. The hot shell structure typically comprises stainless steel sheets welded between machined rings. The forward connection between the turbine and high velocity diffuser typically requires some type of machined slip fit device to accommodate relative thermal growth. This type of flange requires machined parts and is prone to slippage, which can create a forward facing step. The step can catch fuel and allow that fuel to leak out of the connection and soak the external insulation.
The aft end of the high velocity diffuser is typically connected to an internally insulated, low velocity diffuser using some type of expansion joint. The expansion joint must accommodate the relative movement between the turbine and aft diffuser. Some gas turbines have used metal bellows expansion joints in the high velocity area or hot-to-cold insulated transitions. The reliability of the expansion joint over the years has not always been satisfactory. The expansion joints made with soft materials tend to wear out after two to five years and leak exhaust gas. Metal bellows tend to be very large but can accommodate only a small amount of relative movement.
Diffusers have also been designed with a hot to cold transition section. The forward section of the diffuser is externally insulated and the aft section is internally insulated. In between is a transition section with tapered external and tapered internal insulation.
In accordance with the exemplary embodiment of this invention, we have provided a thermally compliant, load bearing interface between an air cooled gas turbine flange and an internally insulated diffuser casing flange in the high velocity section of the exhaust diffuser. The exhaust diffuser includes an outer casing comprised of rolled, carbon steel plate segments, with a forward flange (also comprised of one or more segments) welded to the forward edge of the casing. The casing is made up of a pair of 180xc2x0 casing halves, adapted for attachment by, for example, welding. Each casing half may be made up of one or more segments. If plural segments are used, they are preferably welded along the seam joints between the segments. Circumferential ring stiffeners are welded at axially spaced locations on the exterior surface of the outer casing to rigidify and strengthen the casing.
Axially extending separator bars are welded to the interior surface of the outer casing, in circumferentially spaced relationship. In addition, one circumferentially extending separator bars are located at the forward end of the casing, interconnecting with the axially extending separator bars. These circumferential separator bars are also composed of a plurality of arcuate segments welded to the interior surface of the outer casing. The axial and circumferential separator bars serve to hold and thus maintain orientation of ceramic fiber insulation batts that are installed between the separator bars. The insulation protects the outer casing from the high gas turbine exhaust temperatures that may be in excess of 1200xc2x0 F. The axial and circumferential separator bars are also each provided with radially extending threaded studs that are used to secure the additional components of the liner system.
Thermally compliant round xe2x80x9ctable topsxe2x80x9d are arranged between, and in some instances straddling, the axially extending separator bars at a location spaced from the forward end of the casing. Each xe2x80x9ctable topxe2x80x9d includes a round top platform supported by four legs welded to the interior surface of the outer casing. Each leg is provided with a threaded stud that projects upwardly through oversized holes in the table top. In other words, each top platform is slipped over the projecting studs. These xe2x80x9ctable topsxe2x80x9d are aligned with apertures in the outer casing plate and facilitate the mounting of instrumentation, e.g., exhaust gas rakes and thermocouple radiation shields, used to monitor operation of the gas turbine.
A first layer of stainless steel liner sheets is installed over the separator bars and insulation, with circular cut-outs aligned with the xe2x80x9ctable topsxe2x80x9d where appropriate. The cut-outs are smaller in diameter than the xe2x80x9ctable tops,xe2x80x9d so that the liner sheets partially overlie the xe2x80x9ctable tops,xe2x80x9d with the threaded studs on the legs of the table tops projecting not only through the table tops but also through the liner sheets. The liner sheets are also provided in the form of arcuate segments, with predetermined axial gaps between adjacent sheets. The liner sheets are formed with rows of oversized holes that permit the liner sheets to be arranged over the threaded studs on the separator bars, i.e., the threaded studs project through the holes in the liner sheets.
Liner hold down bars are located over the interior rows of holes on the liner sheets, i.e., all rows excluding the marginal rows along the side edges of the sheets. The hold down bars are also formed with holes to accommodate the threaded studs projecting through the liner sheets. Nut type fasteners are applied to the threaded studs projecting through the hold down bars and tightened, thereby securing the liner sheets in place.
The liner sheets are interconnected by liner splices that overlie the axial gaps between adjacent sheets. The liner splices also include widened areas with holes that align with the nearest xe2x80x9ctable topsxe2x80x9d associated with adjacent liner sheets. Hold down bars are also installed over the liner splices and projecting studs, with nut type fasteners securing the assembly.
The hold down bars on the liner sheets and the liner splices terminate short of the forward end of the liner sheets, leaving a pair of threaded studs in each row (the rows are defined by the axial separator bars) uncovered by the hold down bars. Forward flange liner splices are installed over the front ends of the gaps between adjacent liner sheets, in axial alignment (and in abutment) with the liner splices, utilizing the available threaded studs. Each forward flange liner splice extends forward of the circumferentially extending separator bars and forward of the outer casing flange, terminating at a radially outwardly directed flange portion.
A first forward flange spacer ring, provided in the form of arcuate segments, is installed on the front face of the outer casing flange, extending radially inwardly of the casing flange to a location adjacent the back side of the radial flanges on the forward flange liner splices. The spacer segments are oriented so as to leave gaps between adjacent segments.
A second forward flange spacer ring is installed over the first forward flange spacer. This spacer is also provided as a plurality of arcuate segments, and the segments are arranged to overlap the seams between the segments of the first forward flange spacer. Cut-outs are provided to accommodate the radial flanges on the forward flange liner splices.
A third forward flange spacer ring is then installed over the second flange spacer, again in the form of arcuate segments, with the segments overlapping the seams of the segments in the second forward flange spacer.
The liner system is completed by the installation of a forward nosepiece liner closeout, again in the form of arcuate segments. Each closeout segment contains an axial portion that extends over the forward end of the liner sheets and forward flange liner splices, with holes to receive the first two rows of threaded studs projecting from the forward separator bars and liner plates, and through the forward flange liner splices and nosepiece segments, and again secured with nut-type fasteners. The nosepiece segments also each include a radially outwardly extending flange portion that overlaps the first forward flange spacer and terminates at a location radially inwardly of the third forward flange spacer. Remaining threaded studs projecting through the liner segments, in areas where there are no hold down bars, also receive nut-type fasteners.
Instrumentation rakes and/or radiation shields are installed and the casing halves joined together by welding.
The gas turbine exhaust frame aft flange includes a closeout component that includes a radially inwardly directed flange over which an extended radial flange portion is bolted. This extended radial flange is adapted to abut front faces of the casing nosepiece and third forward flange spacer. Securing bolts are then passed through the aft exhaust frame of the turbine, the extended radial flange portion of the frame, the first, second and third forward flange spacers, and the casing flange and secured by nut-type fasteners, thus establishing a hard, non-slip mounting between the aft exhaust frame and the diffuser.
Accordingly, in one aspect, the invention relates to a gas turbine exhaust diffuser comprising a substantially cylindrical outer casing provided with a forward casing flange; a substantially cylindrical liner spaced radially inwardly of, and secured to, the outer casing; ceramic fiber insulation supported radially between the outer casing and the liner; and a plurality of arcuate liner closeout segments secured to a forward end of the liner and including radial flange portions radially inward and axially forward of the forward casing flange.
In another aspect, the invention relates to a high velocity exhaust gas diffuser adapted for direct connection to an aft flange of a gas turbine exhaust frame comprising a substantially cylindrical outer casing provided with a forward casing flange; a plurality of arcuate liner sheets arranged circumferentially about the outer casing, and spaced radially inwardly of the casing; a plurality of axially extending separator bars between the outer casing and the liner sheets; ceramic fiber insulation batts supported radially between the outer casing and the liner; and a plurality of liner splices attached to the marginal edges of adjacent ones of liner sheets, thus overlapping axial gaps between the adjacent liner sheets.
In still another aspect, the invention relates to a gas turbine exhaust diffuser comprising a substantially cylindrical outer casing provided with a forward casing flange; a substantially cylindrical liner spaced radially inwardly of, and secured to, the outer casing, the liner comprised of a plurality of liner sheets arranged such that axially extending gaps are established between side edges of adjacent liner sheets; ceramic fiber insulation supported radially between the outer casing and the liner; and a plurality of liner splices secured to adjacent ones of the liner sheets, overlying the axially extending gaps, with a corresponding plurality of forward liner splices axially aligned with respective ones of the liner splices and including a forward flange portion extending radially outwardly toward the forward casing flange; and a plurality of forward nosepiece liner closeout segments secured along a forward edge of the liner and including radially inwardly extending flange portions located axially forward of the forward casing flange.
In still another aspect, the invention relates to a gas turbine and exhaust diffuser assembly comprising a gas turbine having an aft exhaust frame; a substantially cylindrical liner spaced radially inwardly of the outer casing flange; a plurality of arcuate closeout segments secured to a forward end of the substantially cylindrical liner, the closeout segments having radially outwardly extending flange portions; and a plurality of forward spacer rings located between the forward casing flange and the radially outwardly extending flange portions such that one of the forward spacer rings is co-planar with the radially outwardly extending flange portions; and wherein the one of the forward spacer rings and the radially outwardly extending flange portions are directly engaged with and secured to an aft flange component of the exhaust frame.
The invention will now be described in detail in conjunction with the drawings identified below.